Week 16 - System Integration
Individual Assignment:
- Design and document the system integration for your final project
This week is about system integration and I will go throigh various aspects of this topic by discussing my final project both at the current prototyping stage and in regards to future improvements.
System Diagram
Here is a system diagram visualizing the main functions of the sun tracker.
I also made a rough assembly tree.
Design
As with all new developments the resources are limited (time, money, material) and I have to deal with a lot of restrictions and limitations. My approach is to try to account for these limitations and also for possible, unexpected delays or failures.
I was very aware of the production processes I could possibly use and the equipment I had access to. My decision to 3D-print as much components as possible can be explained by the following points.
- confident and experienced in 3D modeling and 3d printing
- fast prototyping and spiral development
- huge freedom of design and complex shapes possible
- lightweight but strong components that are weather resistant
During the 3D design process I made sure to create 3D-print friendly parts with round corners, fillets and little need for support. Also the size of the parts was limited by the build volume of the largest printer I had access to - which determined the split plane for the large housing.
This is the first time I used heat inserts and I find it very convenient, even though the price is quite high, compared to standard hex nuts, which can usually be used in a similar way.
Because the part has to be assembled and disassembled, I used mostly standard DIN EN ISO bolts and nuts of various types. Not all sizes and types are available in our local shop, so I had to consider that in my design.
The complete assembly was drawn in Fusion, which gives a good overview about all components, possible interference and I can extract the BOM list and use it for shopping and assembly.
Because I made all the design from scratch, I never had any issues to know how to assemble the machine or to identify the parts. However, it might be clever and easy to establish a part number system with revision number for the next iteration. I could 3D print the part number directly to the parts.
Bill of Materials
I split the BOM up into three tables for better oversight.
Manufactured components
This table lists the components I made myself.
| Pos | Qty | Description | Material | Machine |
|---|---|---|---|---|
| 1 | 1 | Main circuit board | FR1 | Roland MDX-20 |
| 2 | 2 | Encoder breakout board | FR1 | Roland MDX-20 |
| 3 | 2 | GT2 Pulley and wave generator | PETG | Prusa MK4s |
| 4 | 1 | Circular spline vertical | PETG | Prusa MK4s |
| 5 | 1 | Lower body | PETG | Prusa Core One |
| 6 | 2 | Motor bracker NEMA17 | PETG | Prusa MK4s |
| 7 | 1 | Upper body | PETG | Prusa Core One |
| 8 | 2 | Encoder plate | PETG | Prusa MK4s |
| 9 | 1 | Circular spline horizontal | PETG | Prusa Core One |
| 10 | 1 | Shading sphere | PETG | Prusa MK4s |
| 11 | 1 | Cover plate | PETG | Prusa Core One |
| 12 | 1 | Rod end 1 | PETG | Prusa MK4s |
| 13 | 1 | Rod end 2 | PETG | Prusa MK4s |
| 14 | 1 | Rod end 3 | PETG | Prusa MK4s |
| 15 | 1 | Rod end 4 | PETG | Prusa MK4s |
| 16 | 1 | Rod link | PETG | Prusa MK4s |
| 17 | 2 | Flex spline gear | PETG | Prusa MK4s |
| 18 | 1 | O-ring Ø2,5 L=425 | NBR | - |
| 19 | 1 | O-ring Ø2,5 L=660 | NBR | - |
Purchased parts, mechanical
| Pos | Qty | Description | Supplier | Price | Sum |
|---|---|---|---|---|---|
| 1 | 2 | GT2 Timing belt 356mm | MaiLeXun | $1,51 | $3,02 |
| 2 | 2 | GT2 Timing belt pulley 16T | MaiLeXun | $1,11 | $2,22 |
| 3 | 2 | NEMA17HS4401 Stepper Motor | Hanpose | $8,35 | $16,70 |
| 4 | 4 | Ball Bearing 62200-2RS | BCE Bearing | $3,05 | $12,20 |
| 5 | 2 | Ball Bearing 61900-ZZ | BCE Bearing | $0,76 | $1,52 |
| 6 | 4 | Ball Bearing 61821-2RS | BCE Bearing | $12,41 | $49,64 |
| 7 | 2 | Magnet Diametric Ø6 x 3 | DigiKey | $0,72 | $1,44 |
| 8 | 1 | M12 Connector | DigiKey | $10,52 | $10,52 |
| 9 | 1 | Base plate 3mm AISI304 | Local Shop | 7000kr | 7000kr |
| 10 | 8 | M6 Insert Stainless Steel | Mouser | $0,92 | $7,36 |
| 11 | 5 | M5 Insert Stainless Steel | Mouser | $0,69 | $3,45 |
| 12 | 1 | Air Vent IP67 M32x1,5 | Mouser | $27,65 | $27,65 |
| 13 | 1 | Carbon Fibre Tube Ø12mm | Easycomposites | $16,22 | $16,22 |
| 14 | 1 | Carbon Fibre Hexagon Tube 14mm | Easycomposites | $23,07 | $23,07 |
| 15 | 2 | Hex Bolt M10x80 A4-70 | Ísól | 131kr | 262kr |
| 16 | 6 | Hex Nut Nylon M10 A4 | Ísól | 33kr | 198kr |
| 17 | 4 | Socket Head Bolt M10x55 A4-70 | Ísól | 122kr | 488kr |
| 18 | 6 | Button Head Bolt M6x12 | Ísól | 16kr | 96kr |
| 19 | 5 | Button Head Bolt M5x12 | Ísól | 11kr | 55kr |
| 20 | 10 | Hex Nut Nylon M6 A4 | Ísól | 9kr | 90kr. |
| 21 | 2 | Hex Nut Nylon M5 A4 | Ísól | 5kr | 10kr |
| 22 | 4 | Hex Nut Nylon M8 A4 | Ísól | 15kr | 60kr |
| 23 | 1 | Hex Nut M6 A4 | Ísól | 6kr | 6kr |
| 24 | 8 | Socket Head Bolt M6x30 A4-70 | Ísól | 22kr | 176kr |
| 25 | 4 | Hex Head Bolt M8x60 A4-70 | Ísól | 67kr | 268kr |
| 26 | 4 | Hex Head Bolt M6x40 A4-70 | Ísól | 31kr | 124kr |
| 27 | 2 | Socket Head Bolt M6x40 A4-70 | Ísól | 35kr | 70kr |
| 28 | 4 | Oversized Washer M6 A4 | Ísól | 9kr | 36kr |
Purchased Components - Electrical
These are the electrical components (mainly on the PCB).
| Pos | Qty | Part-No | Description | Supplier | Price | Sum |
|---|---|---|---|---|---|---|
| 1 | 1 | PCB Stock FR1 4'' x 6'' | Carbide 3D | $1,0 | $1,0 | |
| 2 | 4 | C1206C104K5RACTU | Capacitor SMD 1206 0,1µF | DigiKey | $0,08 | $0,32 |
| 3 | 2 | EEE-FN1E101UL | Capacitor 100µF | DigiKey | $0,59 | $1,18 |
| 4 | 1 | 150120BS75000 | LED SMD 1206 blue | DigiKey | $0,23 | $0,23 |
| 5 | 2 | JST Connector male 01x05 THT | Adafruit | $0,13 | $0,26 | |
| 6 | 4 | JST Connector male 01x04 THT | Adafruit | $0,13 | $0,52 | |
| 7 | 1 | JST Connector male 01x03 THT | Adafruit | $0,13 | $0,13 | |
| 8 | 1 | JST Connector male 01x02 THT | Adafruit | $0,13 | $0,13 | |
| 9 | 2 | JST Connector female 01x05 | Adafruit | $0,13 | $0,26 | |
| 10 | 4 | JST Connector female 01x04 | Adafruit | $0,13 | $0,52 | |
| 11 | 1 | JST Connector female 01x03 | Adafruit | $0,13 | $0,13 | |
| 12 | 1 | JST Connector female 01x02 | Adafruit | $0,13 | $0,13 | |
| 13 | 1 | 95278-101-04LF | Header 02x02 SWD P2,54 SMD | DigiKey | $0,41 | $0,41 |
| 14 | 4 | RNCP1206FTD1K00 | Resistor SMD 1206 1k | DigiKey | $0,10 | $0,40 |
| 15 | 1 | RC1206JR-07620RL | Resistor SMD 1206 620 | DigiKey | $0,10 | $0,10 |
| 16 | 1 | B3SN-3012P | Switch Tactile Omron | DigiKey | $0,86 | $0,86 |
| 17 | 4 | DRV8251ADDAR | MotorDriver HalfBridge | DigiKey | $1,78 | $7,12 |
| 18 | 1 | AVR128DB32-I/PT | Microprocessor AVR128DB32 | DigiKey | $1,96 | $1,96 |
| 19 | 1 | LM3480IM3X-5.0/NOPB | Voltage Regulator 5 V 100 mA | DigiKey | $1,07 | $1,07 |
| 20 | 4 | RMCF1206ZT0R00 | Jumper SMD 1206 0 OHM | DigiKey | $0,10 | $0,40 |
| 30 | 1 | - | NEO-6M GPS Module | ebay | $6,50 | $6,50 |
| 40 | 2 | TLE5012BE1000XUMA1CT-ND | Hall effect sensor absolute angle | DigiKey | $3,45 | $6,90 |
| 41 | 4 | RC1206FR-07100RL | Resistor SMD 1206 100 | DigiKey | $0,10 | $0,40 |
| 42 | 2 | RMCF1206JT470R | Resistor SMD 1206 470 | DigiKey | $0,10 | $0,20 |
| 43 | 2 | C1206C104K5RACTU | Capacitor SMD 1206 100nF | DigiKey | $0,08 | $0,16 |
Total Cost
The total cost divides and sums up as follows, when considering currency conversion and taxes:
| Category | Sum | Currency | Import Taxes | Amount in USD |
|---|---|---|---|---|
| Purchased parts mechanical | 175,01 | USD | 25% | 218,76 |
| Purchased parts mechanical | 8939 | ISK | - | 68,26 |
| Purchased parts electrical | 32,33 | USD | 25% | 40,41 |
| Purchased filament PETG | 17160 | ISK | - | 131,03 |
| = | $458,46 |
Packaging
The machine is quite compact and can be separated at the split line of the housing into two separate halves. Each half consists of one harmonic drive with encoder and motor and is supposed to be assembled and adjusted seperatly. Once everything is set up, the two halves are bolted together, after connecting the cables to the PCB.
I made an animation to visualize this better.
The PCB is mounted by inserting it into slots in the housing. It is hold down by gravity, because it is required to remove it easily by hand to access the connectors on the back side.
The wire routing is something I have to give a closer look. Right now, the are loose inside the housing, but I might want to fix them to the wall to organize it better.
Fortunately, the machine will be bolted down and won't move out of place, once it is installed.
I didn't pay much attention to the surface finish, but I think the surface does look quite nice as it comes out of the printer. However, for the cover with the logo, I'm going to try the ironing function to give it a shiny, smooth finish.
Testing
There are three important steps I want to conduct.
1. Shaking: To check the connectors, wiring and rigidity of the arm.
2. Environment Place it outside in wind and rain and check for water tightness, moisture ingress, wind load behaviour and heat expansion.
3. Endurance Run the drives for a certain period of time to analyze wear in the gears.
Failure Modes
Motors and drives
It is very likely, that the drives will get blocked at one point / collide with obstacles or freeze / ice. For that case I will incorporate a trip current in the program to shut down the motor in case of overload and also monitor in the software. If the desired position cannot be reached within a certain amount of time / number of steps, it should shut down, to prevent the motors from stalling continously.
Fasteners
All fasteners use either nylon lock nuts or thread locker.
All stainless-steel fasteners in lock nuts use anti-seize paste.
Arm
The arm is obviously a weak point of the whole assembly, as it creates a huge leverage arm. I'm concerned both about people accidently bumping into the arm (which can be avoided by placing it in an access-restricted area on the roof-top), but more concerned about birds trying to use the arm as resting place. I'm not quite sure how to avoid it, but a medium size seagull might block the drive or even break the arm.
Maybe by placing a sign next to the machine?
Corrosion and weather resistance
Corrosion is a big issue in Iceland. We have both very salty air and acidic gases and rain from geothermal areas. I tried to use as many stainless steel parts as possible and tried to protect the carbon steel parts inside the housing. However, a regular replacement of the bearings is likley necessary.
I need to pay special attention to the PCB and remember to protect it with a coating. Corrosion in the connectors can be reduced by filling them with vaseline.
It will be interesting to see how long the 3D printed parts will last outdoors.
Software
The software is what I'm quite concerned about, as coding is not my strong side and I have experienced strange behaviour in former projects.
For this machine an autonomus operation should be secured and also an automatic restart after a loss of power.
This will need some special attention at a later stage.
Repair and spare parts
To keep the machine up and running, I might create a spare part list for crucial items that should be kept in stock.
All 3D printed parts can be reproduced on demand.
The parts that I assume to be the "weak" spots in the system are intentionally designed quite small so they can be replaced quick and easily.
Lifecycle
Repairing of the machine should be relatively easy, but the main question is if all the electronic components will be available in the future. Due to the low cost of the, it might be wise to keep them in stock.
I estimate a lifetime of ten years for the machine. This is the standard amortization period for this type equipment.